<p>Graphitic carbon nitride (CN) and Indium(III) oxide (In₂O₃) are appealing visible-light-driven semiconductor photocatalysts due to their low cost, facile synthesis, and stability. Its applications endured limitations by photocorrosion, an insignificant optical band gap for solar-light applications, and improper distinction between photogenerated electron-hole pairs. A unique ternary nanocomposite (CN/In₂O₃/MoO₃-0.2) was designed to enhance the efficiency of CN and In₂O₃ materials forphotocatalytic H₂ generation and organic contaminant degradation under visible light. The optimized composite showed an exceptional H₂ generation rate of 2706.5 µmol g^− 1 h^− 1, demonstrating substantial synergistic effects among all pristine and composite material. Besides energy generation, the material demonstrated outstanding performance in environmental cleanup, with a 91.4% degradation efficiency of malachite green (MG). The improved catalytic activity stems from the buildind of a Z-scheme heterojunction, which effectively promotes the separation and migration of electric charge carriers while reducing recombination losses. Density functional theory (DFT) confirm the formation of an intensified built-in electric field and Z-scheme charge transfer mechanism in the ternary heterostructure, providing a quantitative explanation for its excellent charge separation capability and photocatalytic activity. Stability experiments validated the reusbbility of photocatalysts, which maintained 77.8% degradation efficiency after five consecutive cycles. Radical scavenging tests showed, during the degradation process, that holes (h⁺) and hydroxyl radicals (·OH) are the main active species. This research provides important insights into the development of multifunctional photocatalysts for sustainable H₂ production and pollutants degradation performance.</p>